Metallo-gallium materials such as gallium-arsenic, gallium-antimony and gallium-arsenic-aluminum are known to have semiconductor properties The intermelallic gallium arsenide species (i.e., GaAs), for example, is particularly attractive as the electron transport therethrough is said to be five times greater than that of silicon and accordingly permits devices to be made therefrom which can operate at higher frequencies than comparable silicon devices, resulting in faster electronics. Moreover, GaAs has a direct band gap that: (1) makes it ideal for many opto-electronic applications such as semiconductor lasers and LED's; and (2) is near the optimum for solar energy conversion. For solar cell applications, GaAs is best utilized as a thin film spread over a large surface area. Electrodeposition would be an ideal way to make such a film.
No commercially practical method has as yet been devised to electrodeposit uncontaminated, equimolar metallo-gallium semiconductor films. In this regard, gallium-arsenic films have been electrocodeposited from: (1) aqueous solutions containing Ga and As ions; (2) AlCl.sub.3 -butylpyridinium chloride or AlCl.sub.3 -1-methyl-3-ethylimidazolium chloride melts (40.degree. C.) containing arsenic and gallium chlorides; (3) potassium tetrachlorogallate melts (300.degree. C.) containing arsenic triiodide; and (4) systems similar to the NaPO.sub.3, NaF, and Ga.sub.2 O.sub.3 fused salts (800.degree. C.) used to deposit GaP. Such processes, however, leave much to be desired Aqueous solutions evolve hydrogen which competes/interferes with codeposition process. The AlCl.sub.3 -pyridinium/imidazolium chloride methods are susceptible to aluminum contamination of the deposit and therefore precludes their practical use in making highly efficient Ga-As semiconductor devices. The potassium tetrachlorogallate and NaPO.sub.3 /NaF/Ga.sub.2 O.sub.3 methods are practiced at temperatures which are unacceptably high in view of: (1) the volatility of arsenic and its salts; and (2) the nature of the materials required to construct thermally durable cells suitable for codepositing the gallium and arsenic. Finally, the lower temperature processes have relatively narrow ranges of operating parameters or ?windows" within which to successfully operate which accordingly makes them difficult to control on a commercially practical basis.